EPITHELIAL TISSUES 9 



near the lower border of the cells. As they approach the 

 surface the layers become flatter and more scale-like and 

 possess less vitality. As the outer layers are worn away the 

 lower more vigorous layers push upward to the surface to 

 take their place. In the middle strata, where the cells are 

 polyhedral in shape, we find the layer of prickle cells which 



FIG. 4. Vertical section of the stratified epithelium of the rabbit's 



cornea. 



a, anterior epithelium, showing the different shapes of the cells at various 

 depths from the free surface; b, a portion of the substance of cornea. (Kirkes 

 after Klein.) 



have minute projecting spines by which they are connected 

 together. This layer is sometimes called the stratum spin- 

 osum. Just below this is the stratum germinativum, or ger- 

 minating layer. 



(2) Columnar Epithelium. (a) The simple columnar va- 

 riety consists of a single layer of column or rod-shaped cells, 

 set upright, longitudinally striated and containing oval-shaped 

 nuclei. This variety is found in the lining of the stomach 

 and intestines. 



(b) In the stratified columnar variety the single layer of 

 cells is replaced by several layers and the superficial elements 

 alone are typical. This type is found in the vas deferens. 

 Ciliated, it occurs in the Eustachian tube, lachrymal ducts, 

 respiratory part of the nasal fossae, ventricle of larynx, tra- 

 chea and bronchi, epididymis and first part of vas deferens. 



(3) Modified Epithelium. (a) Ciliated epithelium is 

 more common with the columnar variety than with any other. 



